This invention relates to composite particles comprising core particles and a silicone elastomer adhered to the surfaces of the core particles, a method for preparing the same, and a cosmetic composition containing the composite particles.
A makeup cosmetic composition such as a foundation is to conceal skin configuration troubles such as wrinkles, pores and texture roughness and skin tone troubles such as blemishes and freckles, and gives a smooth and beautiful look to skin. In recent years, a non-artificial natural finish feel (bare skin feel) is considered to be important. A cosmetic composition is assessed to provide a natural finish feel, when the cosmetic composition is free of unnatural gloss (shine), is excellent in the uniformity of the adhesion of a cosmetic film, and has high transparency. Numerous new materials and new technologies have conventionally been proposed to provide a natural finish feel while retaining the above-described effects of makeup cosmetics. Especially for concealing configuration troubles, cosmetics having various diffuse reflectance powders blended therein are known. Proposed in JP-A 6-128122 (Patent Document 1) is a wrinkle-concealing, multilayer cosmetic making in which a makeup foundation containing a tacky substance for a first layer, and a makeup finish containing a powder that diffuses and reflects light for a second layer are used in combination. In this wrinkle-concealing, multilayer cosmetic, composite powder of the light diffuse reflectance type obtained by coating talc particles with an acrylic polymer is used, for example.
This cosmetic composition is, however, accompanied by a drawback that, when a cosmetic film is held for a long time on the skin, the powder and the tacky substance fall outside an appropriate mixing range due to mixing of sebum to the tacky substance, leading to reductions in its effects. The pamphlet of PCT Patent Publication No. WO 92/03119 (Patent Document 2) discloses a flaky fine powder composed of a flaky substance such as natural mica and spherical, fine particulate silica coated on the surfaces of the flaky substance. Because this flaky fine powder uses the spherical fine particles having high surface diffuse reflectance effects for light, the use of this flaky fine powder as a cosmetic additive is described to bring about technical effects that “the gloss of mica as a base at corners thereof can be reduced, a soft focus effect such as making fine wrinkles less noticeable can be exhibited, and further, cosmetics far improved in slipperiness and touch feel in use can be obtained.”
For the extremely good slipperiness of the flaky fine powder, however, a cosmetic composition having the flaky fine powder blended therein involves a drawback that it tends to form creases upon application, can be hardly applied evenly, and cannot obtain a natural finish. In addition, the fine particulate silica employed as a coating material decreases the area of contact between the composite powder and the skin. The cosmetic composition is, therefore, accompanied by another drawback that the fine particulate silica reduces the adhesion to the skin, renders the composite powder susceptible to falling off from the skin by physical impacts such as rubbing by clothing, and lowers the retention of the effects of the cosmetic. Further, any attempt to lower the proportion of the fine particulate silica in the flaky fine powder with a view to improving the adhesion of the composite powder to the skin results in a drawback that the effects for configuration troubles cannot be obtained sufficiently.
Other technologies which are similar to the foregoing technologies and are intended to avoid configuration troubles or to bring about a natural finish feel include a cosmetic composition that contains a pigment of the core-shell structure obtained by coating a flaky extender pigment as cores with a colored-pigment-containing titanium dioxide and further coating the coated cores with a light-diffusing powder (JP-A 8-188723; Patent Document 3), a technology that mixes in a cosmetic composition composite powder obtained by coating surfaces of a clay mineral with an inorganic metal hydroxide such as aluminum hydroxide (JP-A 9-20609, Patent Document 4; JP-A 2002-146238, Patent Document 5), a cosmetic composition that contains powder having layers of a high-refractive-index metal oxide coated on surfaces of powder having a refractive index of from 1.6 to 1.7 such as barium sulfate and layers of one or more materials, which are selected from yellow iron oxide, black iron oxide and red iron oxide, coated on the first-mentioned layers (JP-A 2003-40737, Patent Document 6), a cosmetic composition obtained by mixing in the cosmetic composition a silica-zinc oxide composite material obtained by combining silica sol and zinc oxide (Japanese Patent No. 3702072, Patent Document 7).
These composite powders each exhibit a certain degree of soft focus effect owing to their light diffusing effect. When attention is paid to a feel upon use of each cosmetic composition, however, the cosmetic composition is not fully satisfactory in softness, moistness, and smoothness for the hardness of the composite powder itself because the composite powder is composed of the inorganic metal oxide or inorganic metal hydroxide. For the purpose of improving the feel on use of such a cosmetic powder, specifically, imparting a feel on use such as a freely flowing feel and smoothness, spreadability, adhesiveness and the like, on the other hand, JP-A 2002-69329 (Patent Document 8) proposes particles obtained by coating surfaces of scaly inorganic particles with a polyurethane, styrene-butadiene copolymer, silicone-based elastomer or polyolefin-based elastomer, and describes that a soft and moist feel can be obtained.
However, no specific exemplification is made as to the particles coated with such a silicone-based elastomer. In yet further documents, particles with silicone elastomers coated on surfaces of particles and their making methods are proposed. Proposed in JP-A 8-3451 (Patent Document 9) is a method that mixes a silicone elastomer having reactive functional groups and silica to crush them. This method is, however, accompanied by a drawback that, because the silica particles as core particles are crushed, particles cannot be obtained with the initial shape and particle size. In other words, particles in the form of a specific shape such as sphere, plate or rod cannot be obtained, and the particle size can be hardly controlled. JP-A 3-294357 (Patent Document 10) proposes a method that mixes core particles with a curable silicone composition which would cure into a silicone elastomer, and then cures the silicone composition. The resulting particles, however, contain plural core particles therein. JP-A 2-232263 (Patent Document 11) proposes a method that emulsifies and disperses in water a mixture of silica particles as core particles and a curable silicone composition which would cure into a silicone elastomer and then cures the silicone composition, and JP-A 3-281536 (Patent Document 12) proposes a method that emulsifies and disperses in water a mixture of an aqueous dispersion of silica particles and a curable silicone composition which would cure into a silicone elastomer and then cures the silicone composition. These methods, however, form particles containing plural core particles therein or particles containing no core particles therein.